Conversion of saturated carboxylic acids to n-alkylated aldimines

ABSTRACT

THIS INVENTION RELATES TO A PROCESS WHEREBY SATURATED ALIPHATIC CARBOXYLIC ACIDS OR THEIR PREFORMED METAL SALTS ARE CONVERTED TO THEIR CORRESPONDING N-METHYLALDIMINE OR N-ETHYLALDIMINE ANALOGS. MORE SPECIFICALLY, THIS PROCESS INVOLVES TREATING THE CARBOXYLIC ACID OR ITS PREFORMED METAL SALT IN METHYLAMINE OR ETHYLAMINE WITH LITHIUM METAL TO FORM ITS ANALOGOUS N-METHYLALDIMINE OR NETHYLALDIMINE. THE EXISTING METHODS FOR THE PREPARATION OF N-ALKYLTED ALDIMINES FROM CARBOXYLIC ACIDS INVOLVES THE INITIAL CONVERSION OF THE CARBOXYLIC ACID TO ITS ALDEHYDE ANALOG (WHICH USUALLY INVOLVES SEVERAL DISCRETE STEPS) FOLLOWED BY REACTION OF THE ALDEHYDE WITH A PRIMARY AMINE TO PRODUCE THE N-ALKYLATED ALDIMINE. IT IS THE OBJECT OF THE PRESENT INVENTION TO PROVIDE A PROCESS WHEREBY THIS CONVERSION OF A CARBOXYLIC ACID TO THE N-METHYLALDIMINE OR N-ETHYLALDIMINE MAY BE EFFECTED IN A SINGLE DIRECT STEP. IT HAS BEEN FOUND THAT THE OBJECT OF THE INVENTION MAY BE ACCOMPLISHED BY REACTION OF A SOLUTION OF THE ACID OR ITS METAL SALT IN METHYLAMINE OR ETHYLAMINE WITH LITHIUM METAL AND MAINTAINING NON-ACIDIC CONDITIONS DURING THE PRODUCT ISOLATION PROCEDURE.

United States Patent 3,819,704 CONVERSION OF SATURATED CARBOXYLIC ACIDSTO N-ALKYLATED ALDIMINES James D. Adkins, 9800 E. Bluegrass Parkway,.lelfersontown, Ky. 40299; Angela O. Bedenbaugh and John H. Bedenbaugh,both of Box 466, Southern Station, Hattiesburg, Miss. 39401; and W. A.Bergin, 1812 Orso Drive, Laurel, Miss. 39440 No Drawing. Filed Feb. 5,1971, Ser. No. 113,076 Int. Cl. C07c 119/00 US. Cl. 260-566 R 3 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to a process wherebysaturated aliphatic carboxylic acids or their preformed metal salts areconverted to their corresponding N-methylaldimine or N-ethylaldimineanalogs. More specifically, this process involves treating thecarboxylic acid or its preformed metal salt in methylamine or ethylaminewith lithium metal to form its analogous N-methylaldimine or N-ethylaldimine.

The existing methods for the preparation of N-alkylated aldimines fromcarboxylic acids involves the initial conversion of the carboxylic acidto its aldehyde analog (which usually involves several discrete steps)followed by reaction of the aldehyde with a primary amine to produce theN-alkylated aldimine. It is the object of the present invention toprovide a process whereby this conversion of a carboxylic acid to theN-methylaldimine or N-ethylaldimine may be effected in a single directstep.

It has been found that the object of the invention may be accomplishedby reaction of a solution of the acid or its metal salt in methylamineor ethylamine with lithium metal and maintaining non-acidic conditionsduring the product isolation procedure.

DISCLOSURE This invention relates to a process for converting certainsaturated aliphatic carboxylic acids into their correspondingN-methylaldimine or N-ethylaldimine analogs.

The prior state of the art is defined by the patent, US. 1,834,850,patented Dec. 1, 1931 and granted to Walter Kropp. This patent disclosesa process for the preparation of unsaturated aldimines by condensingalpha-beta-substituted acroleins with primary aromatic amines.

This invention is totally unlike the process described in the citedpatent in that a saturated carboxylic acid, rather than an unsaturatedaldehyde, is a reactant. Moreover a primary aliphatic amine, rather thana primary aromatic amine, is employed in this invention. Finally atotally difierent type of chemical reaction is involved in thisinvention, namely reduction of a carboxylic acid rather thancondensation of an aldehyde with an amine.

The acids suitably employed in the process of this invention arestraight chain or branched chain saturated aliphatic carboxylic acidscontaining three or more carbon atoms. Best results are obtained withacids containing more than five carbon atoms. The acids may be usedeither in the form of the pure acid or in the form of its metal salt. Ifthe free acid or the salt of a metal other than lithium is used, itslithium salt is formed vin situ.

In the process lithium is preferably employed in a slightly greater than3 :1 molar ratio of lithium to carboxyl group. Thus 3 gram-atoms oflithium are necessary to convert 1 mole of a saturated monocarboxylicacid to its aldimine analog or 6 gram-atoms are required to convert 1mole of a saturated dicarboxylic acid to the dialdimine. If the lithiumsalt of the acid is used, 2 gram-atoms of lithium are required for theconversion of monacid to aldimine; however, if other metal salts areused, 3 gram 3,819,704 Patented June 25, 1974 'ice,

atoms of lithium are required because the other metal precipitates asthe first gram-atom of lithium is added.

The process of the invention is conducted by the addition of the properamount of lithium metal to a solution of the carboxylic acid or its saltin methylamine or ethylamine. Alternatively the carboxylic acid or itssalt may be added to a solution of lithium in methylamine or ethylamine.The usual temperature of the process is that of refluxing amine, about-6 C. for methylamine and approximately 17 C. for ethylamine. Theprocess is typically conducted at atmospheric pressure, but greaterpressures are not prohibited. After eight hours or loss of bluecoloration, the reaction is quenched by addition of water, ammoniumchloride, alcohol or a mixture of these compounds, the solutionsremaining basic under these conditions. (When non-lithium salts areused, the precipitated metals are recovered best by mechanical methodsprior to quenching.) From the resulting solution the amine solvent maythen be recovered by distillation. The N- alkylated aldimine product ofthe process may be obtained by distillation or extraction with suitablesolvents such as pentane or diethyl ether. Any unreacted acid remainingin the reaction vessel after removal of the aldimine product may berecovered from its metal salt by acidification of the solution andextraction. The lithium used in the reaction can be recovered in theform of a salt.

The product of the process is an N-methylor an N- ethylaldimine. Forexample, from the reaction of lithium with pentanoic acid in methylamineis obtained N-pentylidenemethylamine; from lithium with decanoic acid inethylamine is obtained N-decylidenethylamine, etc.

A series of reductions of saturated carboxylic acids was conductedemploying methylamine and lithium metal. Typically the acid wasdissolved in the methylamine solvent and the lithium metal added to thesolution. The mixture was stirred until the blue color disappeared orfor 8 hours for monoacids and up to 15 hours for diacids. The reactionwas then quenched with water, extracted with pentane or diethyl etherand the product isolated by distillation and analyzed by gas-liquidchromatography. The results of this series are shown in Table I.

TABLE I Lithium Methyl- Reaction Percent Amount amine time conver- Acrd(moles) atoms) (m1 (hrs.) sion Propiome 0. 250 0. 750 500 3. 5 15Butyric- 0. 250 0. 750 500 5 21 Pentanoie 0. 250 0. 750 500 4. 5 68Neopentanoic. 0. 250 0. 750 500 3 15 Neoheptanoie. 0. 250 0. 750 500 362 Oetanoic. 0. 250 0. 750 500 2 59 Decanoic. 0. 250 0. 750 1000 7. 5 69Dodecano 0. 10 0. 30 600 8 61 Tetradecanoic 0. 062 0. 314 600 8 84Hexadecanoic 0. 062 0. 25 600 6. 5 33 Octadecanoic. 0. 062 0. 25 1000 8Trace Cyelohexanoic 0. 250 0. 810 500 5 65 Isopentanoic 0.250 0 810 5008 43 Butandioic 0. 250 1. 50 1000 8 15 Hexandioic- 0. 250 1. 50 1000 825 Nonandioic 0. 250 1. 50 1000 12 58 EXAMPLE II A series of reactionswas conducted by the procedure of Example I with ethylamine as thesolvent.

3 EXAMPLE In A series of reactions was conducted by the procedure ofExample I but using the lithium, sodium, iron, and potassium salts.

1. A process for converting the lithium salt of a saturatedunsubstituted aliphatic mono or di carboxylic acid containing 3 or morecarbon atoms to the corresponding N-methylaldimine or N-ethylaldimineanalog which comprises reacting at reflux temperature a methylamine orethylamine solution of said carboxylic acid lithium salt with lithiummetal in at least 2:1 mole ratio amounts relative to the carboxylic acidsalt groupings of the carboxylic acid salt and recovering theN-methylaldimine or the N-ethylaldimine from the reaction mixture.

2. A process according to claim 1 wherein the lithium salt is formed insitu by reacting said carboxylic acid with lithium metal in at least 3:1mole ratio amounts relative to the free carboxyl groups of the acid.

3. A process according to claim 1 wherein the lithium salt is formed insitu by reacting a metal salt, other than the lithium salt, of saidcarboxylic acid with lithium metal in at least 3:1 mole ratio amountsrelative to the free carboxyl groups of the acid.

References Cited UNITED STATES PATENTS 1,834,850 12/1931 Kropp 260566FOREIGN PATENTS 538,523 8/1941 Great Britain. 817,153 8/1937 France.819,577 10/1937 France.

6,616 8/1957 Japan. 1,010,496 6/1957 Germany.

OTHER REFERENCES Sprung, Chem. Rev., 335 (1940). Tiollais, Bull. Soc.Chim. France, 708 (1947). Chancel, Compt, Rend. 233 (1894). Layer, Chem.Rev., 497 (1963). Valli-Douau, Rev. parfumerie, 224 (1925). Snell etal., Dictionary of Commercial Chemicals, pp.

Tiollais, Bull. Soc. Chim. France, 959 (1947). Campbell et al., I. Am.Chem. Soc., 82 (1944).

HOWARD T. MARS, Primary Examiner 30 G. A. SCHWARTZ, Assistant Examiner

